The SRD5A2 gene helps the body convert testosterone into dihydrotestosterone, a hormone signal that supports development of the external genitals before birth and later affects prostate growth, body hair, and puberty changes. If this gene does not work well, a person with XY chromosomes may be born with genital differences and may have less facial or body hair later on. This gene plays an important role in how medicines such as finasteride and dutasteride work.
What is a gene?
Genes are sections of DNA that carry instructions your cells use to make molecules or regulate processes in the body. Some genes hold the information needed to produce proteins, the parts of cells that do the work. Other genes mainly control when certain processes happen, where they take place, and how strongly they occur. Taken together, genes affect how the body develops and functions, and they can influence how you respond to food, stress, or medications. To go into this topic in more detail, you can find more in the LearnHub.
Overview
SRD5A2Gene function
What if the gene works
The SRD5A2 gene makes an enzyme that converts testosterone into dihydrotestosterone, a stronger androgen. This helps typical development of external male sex organs before birth and supports some puberty changes, including prostate growth and body hair.
Risk
What if the gene does not work
Variants in the SRD5A2 gene can reduce activation of testosterone before birth, causing 46,XY differences in sex development. Effects can range from milder genital differences to more marked undervirilization, and puberty may bring further masculinization.
Treatment
What does that mean for your treatment
Pathogenic variants in the SRD5A2 gene can influence hormone treatment choices. In people with SRD5A2 deficiency, clinicians may use dihydrotestosterone (DHT) or testosterone to support genital development and pubertal changes, with the choice guided by age, anatomy, and the person’s goals. No other SRD5A2-specific drug approach is currently established.
Conditions associated with SRD5A2
Gene function
What if the gene works
Understanding the normal function of the SRD5A2 gene helps explain how certain tissues respond to male sex hormones. In everyday cell activity, this gene changes testosterone into a stronger form called dihydrotestosterone, or DHT. That local hormone signal supports typical development and ongoing activity in tissues such as the prostate, skin, and external genital area.
The SRD5A2 gene helps cells convert testosterone into dihydrotestosterone, or DHT. DHT gives a stronger androgen (male sex hormone) signal in tissues that rely on it.
This hormone change happens mainly inside certain tissues rather than evenly throughout the whole body. It gives places like the prostate, external genital tissues, and some skin cells a more focused signal.
DHT made through the SRD5A2 gene supports normal development and day to day function in androgen sensitive tissues. This is especially important before birth and later in tissues such as the prostate and external genital area.
What is a variant?
A genetic variant is a minor difference in the DNA sequence within a gene. These differences are common and are part of normal human diversity, including variation in appearance, metabolism, and the way the body reacts to environmental factors. Many variants do not have any obvious effect and are simply part of natural genetic variation. At times, though, a variant changes how a gene works more significantly and may contribute to or cause a genetic condition.
Genetic variants
What if the gene does not work
Variants in the SRD5A2 gene can reduce or block 5-alpha-reductase type 2 activity, so cells make less dihydrotestosterone from testosterone. Some SRD5A2 gene variants mainly weaken enzyme stability or folding, while more severe variants leave little or no working enzyme. This range in functional effect helps explain why 5-alpha reductase type 2 deficiency can vary, with milder or more pronounced differences in sex development.
How variants are linked to conditions
Pathogenic variants in the SRD5A2 gene cause 5-alpha reductase 2 deficiency, a condition that affects sex development in some people with 46,XY chromosomes. This well-established SRD5A2 gene condition is linked to differences in genital development before birth and may become more noticeable at puberty. Two pathogenic variants, one inherited from each parent, are typically needed to confirm the diagnosis.
A variant is not necessarily a diagnosis
Genetic variants are a usual part of human biology and are common across the general population. Most do not have a direct effect on health and simply contribute to natural human diversity. For many genes, having a variant associated with a condition indicates a possible link rather than a definite diagnosis, especially when several genes and environmental factors are involved. In some situations, though, a single well-characterized variant in a particular gene is enough to confirm a diagnosis.
Are there things that can increase or change my risk?
For SRD5A2, risk is mainly set by the gene change itself rather than lifestyle. A child’s chance of having the condition is higher when both biological parents carry an SRD5A2 variant, and it can also be higher when parents are blood relatives; there is not enough evidence that diet, exercise, or supplements lower this genetic risk.
Inheritance of SRD5A2 variants
Variants in the SRD5A2 gene linked to 5α-reductase 2 deficiency are inherited in an autosomal recessive pattern. This means a child usually inherits one altered copy from each parent, while parents with one altered copy are typically carriers. When both parents carry an SRD5A2 variant, each pregnancy has a 25% chance of being affected, a 50% chance of resulting in a carrier child, and a 25% chance of inheriting neither variant. The SRD5A2 inheritance pattern is the same for males and females because this gene is on chromosome 2, not a sex chromosome.
What does my SRD5A2 result mean for my family?
Changes in the SRD5A2 gene are usually passed down in a recessive pattern, which means close relatives may be carriers even if they have no symptoms. Brothers or sisters could also have the same condition or carry the same gene change. For family members planning children, carrier testing can help clarify whether the change may be passed on in the next generation.
Genetic information
Genetic testing
How you find out about variants
SRD5A2 genetic testing checks DNA from a blood, saliva, or cheek swab sample for variants in the SRD5A2 gene. Results may identify a known variant, show no relevant variant, or find a variant whose meaning is still unclear. Testing can help confirm or rule out an SRD5A2-related diagnosis.
When should I consider getting a genetic test?
Consider SRD5A2 testing if a baby is born with genitals that do not look typically male or female, or if someone raised as a girl develops clear male-type changes at puberty. It may also help when this condition runs in the family or when there are unexplained fertility problems in men.
A genetic result is only one part of your health story
How informative a genetic result is depends on both the condition and the kind of variant found, although it can still provide valuable insight. Over time, the way the body functions is also shaped by factors like age, lifestyle, environment, and medical history. In conditions affected by many genes, genetic information usually offers context rather than certainty and makes the most sense when considered with the rest of a person’s care. In other situations, the result may give a clear answer. For areas like medication response, genetic findings can help put personal experiences in context.
Pharmacogenetics
How variants shape your response to medicine
Genetic variation can affect how people respond to medicines. Some people break down a drug more slowly or more quickly, while others may be more or less sensitive to its effects. This helps explain why the same treatment works well for one person but less well for another. These differences are common and can influence both how well a medicine works and the chance of side effects.
What is Pharmacogenetics?
Pharmacogenetics looks at how genetic differences can affect a person’s response to medicines. It studies connections between genes and drugs to help explain why the same treatment may work differently from one person to another. For many medications, genes can influence how the body handles a drug or how strong its effects are. This information can support better informed, more individualized treatment decisions. You can read more about this topic in the LearnHub.
Drugs influenced by the SRD5A2 gene
When should I seek medical advice?
There is not yet a broadly confirmed role for this gene in guiding medication choices, so general questions about symptoms, treatment, or side effects are best discussed with your doctor. SRD5A2 has been studied in relation to response to medicines that block testosterone conversion, such as some treatments for prostate enlargement or hair loss, but this research is not used routinely to direct care.
History
The history of the SRD5A2 gene became especially visible through studies of families in the Dominican Republic during the 1970s, when doctors described children with undervirilized genital development at birth who often developed more typically male features at puberty. Initially understood only through visible traits, later recognized as tied to a specific gene, this pattern helped researchers connect hormone changes to inherited variation. From these first observations, research expanded steadily. By the 1990s, scientists had identified the SRD5A2 gene and linked certain variants to 5 alpha reductase deficiency, a condition affecting sexual development. This work also shaped interest in medicines that block the same enzyme, including finasteride. The way this gene was viewed has shifted over time as understanding of sex development became more precise and respectful.